An on-load tap changer system used with a transformer includes an on-load tap changer having a diverter switch, a tap selector and a changeover selector, and an operating mechanism for operating the on-load tap changer. A tap change operation monitoring apparatus for monitoring tap change operation of this kind of on-load tap changer system is disclosed in Patent Document 1 or Patent Document 2, for example.
A tap change operation monitoring apparatus disclosed in Patent Document 1 includes a torque sensor unit for detecting torque exerted on a drive shaft of an operating mechanism by using a pattern of a sequence of tap change operations, a switching pattern discrimination unit for discriminating switching pattern of tap change operations of a diverter switch, a tap selector and a changeover selector, a normal torque pattern memory unit for storing torque patterns under normal operating conditions for individual switching patterns, an abnormal point discrimination unit for discriminating an abnormal operation point by selecting a normal torque pattern for a specified switching pattern based on an output from the switching pattern discrimination unit and then comparing the selected normal torque pattern with an output from the torque sensor unit, and a normal torque pattern correction unit for correcting memory content of the normal torque pattern memory unit based on a varying tendency of the output of the torque sensor unit representing a torque pattern under normal operating conditions where no operational anomaly is detected.
This apparatus discriminates an abnormal operation point by comparing a tap changing torque pattern at switching action detected by the torque sensor unit during the tap change operation with a tap changing torque pattern under normal operating conditions, detects a tendency for tap changing torque to reduce over time, and corrects the normal torque pattern.
Also, this apparatus determines whether any anomaly exists or not by selecting a normal torque pattern corresponding to each switching pattern and then comparing the normal torque pattern with the output from the torque sensor unit, and specifies an abnormal point from time of occurrence of an anomaly.
A tap change operation monitoring apparatus shown in Patent Document 2 includes current sensing means for detecting motor current in an operating mechanism, torque sensing means for detecting drive shaft torque produced by an on-load tap changer, operating mode discrimination means for discriminating operating mode in which the on-load tap changer performs tap change operation, tap changing data recording means for discriminating and recording motor current waveform data detected by the current sensing means during the tap change operation as well as torque waveform data detected by the torque sensing means for each operating mode, reference data setup means for setting monitoring target specification data for each discriminated operating mode and then presetting and storing reference values of the monitoring target specification data and permissible variable ranges thereof for each operating mode, specification data extraction means for extracting specification data corresponding to the preset monitoring target specification data from the recorded motor current waveform data and torque waveform data, and anomaly judgment means for judging that operating state is abnormal if the permissible variable ranges are exceeded as a result of a comparison between the extracted specification data and the reference values thereof corresponding to the operating mode.
This apparatus assumes operating times of a diverter switch, a tap selector and a changeover selector and presets a specific time period with respect to the torque waveform data detected by the torque sensing means. The apparatus recognizes a point of a maximum value of the waveform within this time period as a specified point and extracts a torque value at this point and time of occurrence thereof. Then, the apparatus compares the extracted values with the reference values stored in the reference data setup means and, if the permissible variable ranges are exceeded, the apparatus judges that the operating state is abnormal. It is therefore possible to make a judgment with simple processing and high accuracy.
Patent Document 1: Japanese Patent Application Publication No. 1992-137511
Patent Document 2: Japanese Patent No. 3189542